282 BULLETIN OP THE BUREAU OP FISHERIES. 



terly way. It is apparent that structure is of great importance, but behavior must 

 also be considered. If not influenced by other factors, fishes will persistently select 

 certain habitats and foods. The most potent influences in changing foods and feeding 

 habits come with the seasonal cycle and with changes in age. The annual succession 

 of seasons brings breeding, changes in gases and minerals in the water, variations in 

 temperature, fluctuations in food supply and shelter, and other things which require 

 variations in behavior. Young fishes do not have to breed and require different foods 

 from adults. Through all these changing influences, food is in general more important 

 than any other single factor in causing fish to select particular habitats. 



VI. GENERAL CONSIDERATIONS OF THE FOODS ON THE SHORE FISHES OF LAKES. 



The food of the 30 lake fishes reported in this paper shows that most species feed 

 along the shore. Young fishes are found more or less in shallow water everywhere, but 

 most of the adults are more specific in their selection of habitats and for the most part 

 frequent the aquatic vegetation, which furnishes food and shelter. The fishes which are 

 not usually associated with shore vegetation live near the bottom (perch, sucker), on 

 rocky or pebbly shores (miller's thumb, Johnny darter), at the surface (silversides), or 

 in the open water (cisco). 



Competition between species for the different kinds of food is usually not very 

 keen. When a particular sort of food is abundant, a number of different fishes may feed 

 upon it, but if it becomes scarce the fishes do not all turn to the same diet for a second 

 choice. This specificity in the selection of food enables different species to live together 

 in the same habitats. 



It is important in considering fish foods and the feeding of fishes to keep in mind 

 that habits change as age increases. Forbes (1888) said, "One-celled organisms and 

 Entomostraca are the natural, and practically the only, food of an undifferentiated 

 small fish ; and to be at liberty to grow, the fish must either change its food (as is usually 

 done) or must develop a special apparatus (commonly a set of fine gill rakers) for the 

 separation of Entomostraca from the waters in which they swim. A few apparently 

 become vegetarians at once; most pass into or through an insectivorous stage. After 

 this a few become nearly omnivorous, like the bullheads; others learn to depend chiefly 

 on moUuscan food — the sheepshead and the redhorse species — but many become essen- 

 tially carnivorous." The great dependence of many species of young fishes on ento- 

 mostracans makes them rivals to some extent for the same foods, but, as Forbes pointed 

 out, this is offset in part by the seasonal differences in the time of hatching. Some fishes 

 also begin to eat small dipterous larvae as soon as they are able to feed. From the data 

 presented in this paper it appears that insect larvae are of as much importance for young 

 fishes as entomostracans. 



Adult fishes fall readily into classes, according to their chief foods — vegetarians, 

 piscivores, insectivores, those that eat entomostracans, and those that feed on mud 

 and sediment. The chief vegetarians in Wisconsin lakes are the carp and sucker. It 

 is an axiom in biology that, in any particular part of the earth, the vegetarians must 

 greatly exceed in numbers the carnivorous animals which feed upon them, and in 

 general this law is fulfilled among the fishes. The insectivorous fishes (basses, darters, 

 etc.) usually secure their food when it is in the larval condition, and, in lakes, adidt 



